Wide-angle pupil relay for cellphone-based fundus camera

ABSTRACT

An optical imaging system includes a first lens system housed in a body of a mobile telecommunication device, the first lens system having a first optical axis, a first entrance pupil fixed in space in a reference plane associated with said body, and a first focal length; and an optical telescope providing a diffraction-limited imaging within a spectral range from at least 486 nm to at least 656 nm. The optical imaging system is configured to image, when the optical telescope is inserted between the first lens system and an entrance pupil of a visual system of an eye (EPE), the EPE onto the first entrance pupil and vice versa with a substantially unit magnification.

The present invention is a Continuation of U.S. patent application Ser.No. 16/288,096, filed Feb. 27, 2019, which is a Continuation of PCTInternational Application No. PCT/JP2017/031412, filed Aug. 31, 2017,which claims priority to US Provisional Patent Application Nos.62/381,768 filed on Aug. 31, 2016, and 62/539,733 filed on Aug. 1, 2017.The disclosures of these applications are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates generally to ocular diagnostic imagingdevices, and more particularly, to a portable handheld smart phone-basedretinal camera, configured to capture high-quality, wide field fundusimages. The use of the mobile phone platform creates a fully embeddedsystem capable of acquisition, storage, and analysis of fundus imagesthat can be directly transmitted from the phone via the wirelesstelecommunication system for remote evaluation.

BACKGROUND ART

Fundus imaging is used extensively in the diagnosis, monitoring, andmanagement of many retinal diseases. One limitation found in currentimaging systems is the bulky and stationary nature of the imagingequipment. Conventional fundus cameras are cumbersome tabletop devicesthat are not readily mobile due to the fragility, large size and heavyweight of these devices. In practice, such fundus cameras also force thepatient to be seated upright, which can be difficult for sick andhospitalized patients. In addition to dimensional constraints, funduscameras require a power source to supply power to the illumination,imaging screen, and data processing unit. Often this power source isprovided by central in-wall power plugs, and continuous electrical poweris required in order for the fundus camera to function properly.

While digital fundus cameras have been envisioned (some of these on thebasis of a cellphone or similar devices such as an iPhone; generally, amobile device), such cameras possess substantial operational limitationscaused by any of (i) a lack of optical conjugation between the opticalsystem of the used mobile device and the vision system being imaged;(ii) an insufficient field-of-view (FOV) associated with imaging of thechosen surface of the vision system, which results in a need formultiple computational “stitching” of the acquired images; (iii) severeresidual aberrations impairing the resulting images, and (iv)combinations of the above.

Accordingly, there remains a need for a low-cost handheld deviceconfigured to function as a substitute for high-cost medical devices andenable the recording of digital images of the surface(s) of a visionsystem during an ophthalmic examination thereof, while being devoid ofthe operational shortcomings characterizing currently known imagingsystem solutions.

SUMMARY OF INVENTION

A first aspect of the present disclosure includes: a first lens systemhoused in a body of a mobile telecommunication device, the first lenssystem having a first optical axis, a first entrance pupil fixed inspace in a reference plane associated with the body, and a first focallength; and an optical telescope providing diffraction-limited imagingwithin a spectral range from at least 486 nm to at least 656 nm whereinthe optical system is configured to image, when the optical telescope isinserted between the first lens system and an entrance pupil of a visualsystem of an eye (EPE), the EPE onto the first entrance pupil and viceversa with a substantially unit magnification.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be more fully understood by referring to thefollowing Detailed Description of Specific Embodiments in conjunctionwith the not-to scale Drawings.

FIG. 1 is a diagram that shows cellphone 20, which is provided withimage capture portion (camera sensor) 214 that captures an image of theeye fundus of a subject eye via window 214W and via an optical systemthat is not shown (image capture lens system (camera lens)), and showsattachment 22, which is attached to cellphone 20.

FIG. 2 is a schematic diagram of the optical train of the firstembodiment complementing the exit pupil of the portable device andrelaying the image of the cellphone camera pupil onto the eye pupil.

FIG. 3 includes spot diagrams characterizing diffraction-limited qualityof imaging with the first embodiment of FIG. 2 for different fieldheights.

FIG. 4 illustrates a second embodiment of an optical train 500,representing an afocal relay system configured to the idea of theinvention, and shown in combination with a Navarro model of a human eye.

FIG. 5 shows spot diagrams of the second embodiment of FIG. 4 fordifferent field heights.

FIG. 6A is a diagram showing a size relationship between an imagecapture field-of-view of the eye fundus and an image sensor in the firstembodiment.

FIG. 6B is a diagram showing a size relationship between an imagecapture field-of-view of the eye fundus and an image sensor in thesecond embodiment.

FIG. 7 is a schematic diagram illustrating the configuration ofattachment 22 according to a third embodiment.

FIG. 8 is a schematic diagram illustrating the configuration ofattachment 22 according to a fourth embodiment.

FIG. 9 is a schematic diagram illustrating the configuration ofattachment 22 according to a fifth embodiment.

FIG. 10 is a diagram illustrating the electrical configuration ofcellphone 20.

FIG. 11 is a flowchart explaining a method of use of attachment 22 andcellphone 20.

Generally, the sizes and relative scales of elements in Drawings may beset to be different from actual ones to appropriately facilitatesimplicity, clarity, and understanding of the Drawings. For the samereason, not all elements present in one Drawing are necessarily shown inanother.

DESCRIPTION OF EMBODIMENTS

FIG. 1 shows cellphone 20, which is provided with image capture portion(camera sensor) 214 that captures an image of the eye fundus of asubject eye via window 214W and via an optical system that is not shown(image capture lens system (camera lens)), and shows attachment 22,which is attached to cellphone 20.

In the explanation of the present invention, a cellphone is identical toa device referred to as a mobile telecommunication device, a mobilephone, or a wireless telecommunication system, and a fundus camera isidentical to a device referred to as a portable handheld smartphone-based retinal camera or a low-cost handheld device.

The cellphone camera lens is the imaging lens on the camera sensor. Ofcourse, these are already provided by cellphone manufacturers.

The present inventor makes use of extremely useful properties of thecellphone camera lens; namely, the lens is approximatelydiffraction-limited, and the entrance pupil is at the front of the lens,just inside the window of the cellphone camera.

If a cellphone has both wide angle and telephoto cameras, these bothhave their entrance pupils substantially in the same location. Thismeans that if the cellphone is mechanically-shifted laterally, eithercellphone camera can be used. Thus, simple zooming is possible without alarge loss of pixels between a 40 dg and 80 dg field-of-view funduscamera.

Another useful feature of cellphone camera lenses is that the fields ofview are similar to what is desired for a fundus camera, so the pupilrelay can be close to 1× magnification, which means that lateralchromatic aberration and distortion can be small, and the optical designrelatively simple.

The coarse focus is a mechanical adjustment of the separation betweenthe lens group G1 and the second lens group G2 to accommodate differentpatients' Diopter settings. The fine focus is the cellphone camera'sbuilt-in autofocus system.

In accordance with disclosed embodiments of the present invention, amodular apparatus and method for use of the same are disclosed for ahandheld, ocular imaging device complemented with an imaging opticaldetection system (a camera), and a programmable processor of a mobilephone, (alternatively, a tablet or another smart device) operablycoupled to optical elements and illumination elements, configured toimage the structure(s) of the eye (such as a retina) in a non-clinicallocation. The modular apparatus provides multi-functionality(fluorescein imaging, fluorescence, bright field, infrared (IR) imaging,near-infrared (NIR) imaging) and multi-region imaging (retinal, corneal,external, etc.) of the eye along with the added features of imageprocessing, storage and wireless data transmission for remote storageand evaluation. Acquired ocular images can also be transmitted directlyfrom the device to the electronic medical records of a patient withoutthe need for an intermediate computer system.

The field of view (FOV) of the retina is a technical specification offundus imaging that is an important consideration in fundus cameradevelopment. The FOV describes the angle through the pupil of an eye atwhich the retina is imaged. The illuminating light from the deviceenters the retina and the reflected light from the retina is used toform an image at the sensor of the device. A standard fundus camera hasan approximately 40-45 degree FOV.

In a digital imaging system disclosed at <peekvision.org/what-it-does>(referred to herein as a Peek system), for example, a cellphone camerais used to take a picture of the user's retina by being placed as closeas possible to the user's eye. In this situation, the entrance pupil(EP) of the cellphone optical system (which is typically located at thefront lens element just inside its front window) is notoptically-conjugate with the user's eye EP or iris (that is, with the EPof the vision system being inspected). (A device that is similarlylimited in configuration and operation is disclosed at<www.d-eyecare.com>.) As a result—as would be readily appreciated by askilled artisan—the image of the retina formed by the employed opticalsystem inevitably contains significant aberrations that, under normaluncorrected/unattended-to circumstances, do not allow the user tocorrectly assess the conditions/status of the imaged retina as intended.In particular, the FOV associated with the imaging of the retina withthe Peek system is, therefore, limited substantially by the ratio of theeye-pupil diameter to the dimension of the foveal region around theoptic nerve and macular region, and the image quality is poor. Whilethis solution provides useful low-cost diagnostic information for someretinal pathologies, it would be advantageous to image a larger area ofthe retina, at higher resolution, such that other more subtle retinalpathologies may be observed.

A fundus camera of Bosch, described at<bosch-eyecare.com/en/eyecare/products/fundus_imaging/fundus_imaging.html>,is also limited to imaging within a +/−40 degree FOV; Jedmed describes asimilar system: <jedmed.com/products/portable-fundus-camera>. A solutionprovided by Volk Optical is another example (see<veatchinstruments.com/Volk-Pictor-Plus-Portable-Retinal-Camera>) of anoperationally-limited system in terms of imaging the retinal surface.

The operational problems associated with existing fundus cameras of therelated art (possessing low FOV, which results in the need for multiplecomputational “stitching” of optical data acquired from a retina, andsubstantial residual aberrations, causing detrimental reduction in theoverall quality of the resulting “stitched” image) are solved byproviding a compact, low cost Fundus camera with a wide 80 degree (fullangle) FOV configured as an achromatic afocal relay (telescope)operating at a magnification level close to 1× to effectuate imaging ofa 2 mm diameter (undilated) eye pupil into the spatially-fixed EP of theoptical system of the mobile device with a diffraction-limitedresolution.

Embodiments of the present invention take advantage of the parameters ofa typical, built-in imaging optical system of a cellphone (or anothermobile device), which possesses a full-angle FOV of about 75 to 80degrees and is assumed to have no aberrations or vignetting (which is areasonable assumption considering the nominal diffraction-limitedperformance of such optical systems as known in the art) and an EP sizeof about 2 mm in diameter (the EP of the mobile device being fixed inspace), to provide an approximately 1× optical relay system for imagingthe EP of the eye to the EP of the mobile device.

Considering the dimensional match, typically available between the EP ofthe undiluted eye and that of the optical system of the typical mobiledevice, the afocal relay of the invention is structured to provideimaging with approximately 1× magnification, thereby ensuring afull-angle FOV at the entrance of the eye of about 80 degrees. This isabout twice that of a typical Fundus camera of the related art and abouthalf the full horizontal field of view of the human eye. Therefore, asingle imaging exposure with the use of the lens of the invention coversa substantially larger area of the retina than a typical fundus camera.Moreover, in the case that spatial stitching of several (for example,four) shots of images of the retina procured with the lens system of theinvention is attempted, not only would the “stitched” image cover thewhole retina, but the stitching would be available while maintaining analmost 50% overlap between stitched individual fields. A person of skillin the art will readily appreciate that such spatial overlap ofconstituent individual images is not possible with the use of a systemdescribed in the related art. Because existing systems have a muchsmaller field of view, 40 degrees or less, one has to overlap many moreindividual images (acquired with an existing system) to cover the wholeretina (about 160 degrees), or, alternatively, to have a smalleroverlap. However, it is recognized in the art that the larger theoverlap between or among the constituent images, the better the qualityof the resulting stitched image, because there are more features (mostlyblood vessels in case of imaging the retina) to use for alignment. Theadvantage of the present embodiment is that each individual constituentimage covers more of the retinal surface, so that one can afford toincrease the area of the overlap between the constituent images whenforming the resulting stitched image.

FIG. 2 shows a Y-Z cross section through an implementation of a lenssystem of the first embodiment-here, configured as arotationally-symmetrical dioptric afocal relay (telescope). Forconvenience, as shown, rays are traced from the cellphone camera EP onthe right of FIG. 2 through the optical system in attachment 22, to aNavarro model eye on the left of FIG. 2 . The lens element closest tothe cellphone camera pupil is labeled as element 1 in FIG. 2 ; the nextlens element is element 2, and so on, while the retinal surface isreferred to as an image plane. The design includes two cemented doublets(320 by the EP of the eye and 310 by the EP of the cellphone cameralens), while the single positive biconvex lens 3 has the highestconverging power among the optical elements present in the embodiment.The cemented doublet lens 320 is composed of a positive meniscus lenselement 6 concave to the eye side cemented with a meniscus lens elementconcave to the eye side. The first lens group G1 includes the cementeddoublet lens 320 and a positive meniscus lens element 4 concave to theeye side. The cemented doublet lens 310 is composed of a biconcavenegative lens element 1 cemented with a biconvex positive lens element2. The second lens group G2 includes the cemented doublet lens 310 and apositive biconvex lens element 3.

Working close to 1× magnification is desirable and provides clearoperational advantages over the systems of the related art, as suchoptical configuration facilitates the correction of lateral color anddistortion aberrations, in stark contradistinction with the systems ofthe related art. The optical design of FIG. 2 is configured tocompensate for the aberrations of the (Navarro model) eye (at 2 mm eyepupil diameter, the healthy human eye is almost diffraction-limited) andprovides close to diffraction-limited resolution across the entire 80degree FOV. The evidence of this operational characteristic is providedin FIG. 3 , which shows ray aberrations (spot diagrams) in the planesthat are locally tangential to the spherical retina, at three identifiedwavelengths, 643.85 nm, 546.1 nm, and 479.99 nm. As shown in FIG. 3 andconvincingly evidenced by the spot diagrams falling within the Airy diskcurve for each of the wavelengths, aberrations are substantiallycorrected over the whole visible spectrum, but are even smaller at thered end of the spectrum (where the backscattered light from the retinais about five times stronger than that in the blue, which isoperationally preferred during the imaging of the retina). Suchdiffraction-limited performance across the visible spectrum criticallyand advantageously distinguishes the proposed invention from that of therelated art. In practice, the proposed design of the optical system issuch that diffraction-limited imaging of the retina is effectuated bybalancing of optical aberrations typical for an average eye with thoseof the eye piece portion of the embodiment of the invention.

Several notes are in order concerning an objective utilized in anembodiment of the system of the invention. Tables 1, 2, and 3 providedata representing an optical train (sequence) of lens elements of thefirst embodiment of FIG. 2 , and Table 4, 5 and 6 provide datarepresenting an optical train (sequence) of lens elements of the secondembodiment of FIG. 4 , forming lens systems configured according to theidea of the invention. The design prescriptions for the embodiments weregenerated with Code V and are discussed in reference to thecorresponding Drawings. In these Tables, optical elements and, possibly,media separating some of the elements, are numbered in a “backward”fashion, starting from that which is the closest to the object/targetplane (illustrated in FIG. 4 ) towards the retinal surface of an eye.This approach to the numbering of the optical elements makes it easier,as would be appreciated by a skilled artisan, to define the NA andparameters characterizing the behavior of the system in the imagespace—that is, in the space of the eye—during the process of opticaldesign. The closest lens element to the object is labeled as element 1both in Table 4 and FIG. 4 ; the next lens element is element 2, and soon, while the retinal surface is referred to as an image plane. Notably,the combination with the Navarro model of the human eye is chosen, thetypical optical properties and geometrical characteristics of which haveto be included in the design of the relay system of the invention forproper assessment of the system.

Positive radius value for a Liven surface indicates that the center ofcurvature of this surface is to the left of the surface, while anegative radius value indicates that the center of curvature is to theright of the surface; dimensions are provided in millimeters; thicknessis defined as an axial distance from a given surface to the nextsurface; and an indicated image diameter is a paraxial value and not aray-traced value. Additionally, with respect to the description ofchromatic aberrations—if present—a reduction in Strehl ratio betweenmonochromatic and polychromatic designs represents the contrast lossfrom chromatic aberrations over the specified spectral band, while avariation in best individual focus shows the residual field curvature.

For the purposes of this disclosure and the appended claims, the use ofthe terms “substantially”, “approximately”, “about” and similar terms inreference to a descriptor of a value, element, property orcharacteristic at hand is intended to emphasize that the value, element,property, or characteristic referred to, while not necessarily beingexactly as stated, would nevertheless be considered, for practicalpurposes, as stated by a person of skill in the art. These terms, asapplied to a specified characteristic or quality descriptor, mean“mostly”, “mainly”, “considerably”, “by and large”, “essentially”, “togreat or significant extent”, “largely but not necessarily wholly thesame” such as to reasonably denote language of approximation anddescribe the specified characteristic or descriptor so that its scopewould be understood by a person of ordinary skill in the art. When usedin reference to a numerical value, the terms represent a range of plusor minus 20% with respect to the specified value, more preferably plusor minus 10%, even more preferably plus or minus 5%, and most preferablyplus or minus 2% with respect to the specified value.

The use of these terms in describing a chosen characteristic or conceptneither implies nor provides any basis for indefiniteness and for addinga numerical limitation to the specified characteristic or descriptor. Asunderstood by a skilled artisan, the practical deviation of the exactvalue or characteristic of such value, element, or property from thatstated falls and may vary within a numerical range defined by anexperimental measurement error that is typical when using a measurementmethod accepted in the art for such purposes. In some specific cases,which are within the scope of the invention, the terms “approximately”and “about”, when used in reference to a numerical value, represent arange of plus or minus 20% with respect to the specified value, morepreferably plus or minus 10%, even more preferably plus or minus 5%, andmost preferably plus or minus 2% with respect to the specified value.

TABLE 1 (Embodiment 1) ELEMENT RADIUS OF CURVATURE APERTURE DIAMETERNUMBER FRONT BACK THICKNESS FRONT BACK nd Vd OBJECT ∞ INFINITY 2.0000APERTURE STOP 6.3116 1 −14.2165 CC    51.3347 CC 2.9966 9.6557 14.26801.846 23.8 2 51.3347 CX −19.9198 CX 18.0063 14.2680 28.6892 1.677 55.19.1964 3 61.3624 CX A(1) 15.0162 44.9001 46.1126 1.517 64.2 54.833843.1273 30.8400 4 A(2) 111.1392 CC 14.4372 43.2966 39.5928 1.517 64.21.0000 5 27.7511 CX  22.3289 CC 7.2581 35.9187 29.2285 1.922 20.8 622.3289 CX 100.0000 CC 8.2817 29.2285 25.5733 1.640 60.1 10.0000 10.15547 Navarro eye model 2.0900 NOTES Positive radius indicates the center ofcurvature is to the right Negative radius indicates the center ofcurvature is to the left Dimensions are given in millimeters Thicknessis axial distance to next surface The Navarro eye model is described inJ Opt Soc Am A. 1985 August; 2(8): 1273-81. Accommodation-dependentmodel of the human eye with aspherics. Navarro R, Santamaria J. BescosJ.

TABLE 2 ASPHERIC CONSTANTS Z = ((CURV)*Y²)/(1 + [1 − (1 +K)*(CURV)²Y²]^(1/2)) + (A)*Y⁴ + (B)*Y⁶ + (C)*Y⁸ + (D)*Y¹⁰ ASPHERIC CURVK A B C D A(1) −0.02129068 −4.40856200 −2.07205E−07  6.94266E−10−9.25536E−14 0.00000E+00 A(2) 0.03723186 −0.99124670  3.54873E−06−1.20826E−09 −1.41664E−12 0.00000E+00 REFERENCE WAVELENGTH = 587.6 NMSPECTRAL REGION = 486.1-656.3 NM

TABLE 3 INFINITE CONJUGATES EFL = −22.2382 BFL = 12.1279 FFL = −18.1278F/NO = −8.3228 IMAGE DIST = 12.0500 OAL = 192.1880 PARAXIAL IMAGE HT =11.6554 SEMI-FIELD ANGLE = 35.0000 ENTR PUPIL DIAMETER = 2.0000 DISTANCE= 0.0000 EXIT PUPIL DIAMETER = 1.8365 DISTANCE = −8.2919 NOTES FFL ismeasured from the first surface BFL is measured from the last surface

TABLE 4 (Embodiment 2) ELEMENT RADIUS OF CURVATURE APERTURE DIAMETERNUMBER FRONT BACK THICKNESS FRONT BACK nd Vd OBJECT ∞ INFINITY 2.0000APERTURE STOP 30.0000 1 −20.8494 CC  102.4570 CC 3.5877 25.6282 36.86751.688 31.2 2 102.4570 CX −32.3754 CX 16.7148 36.8675 43.7003 1.788 47.31.1911 3 158.0684 CX A(1) 12.0000 49.9597 50.9992 1.788 47.3 66.638150.3388 37.0080 4  68.0998 CX INF 14.4000 50.8799 47.7850 1.788 47.31.2000 5  29.7274 CX  60.2508 CC 12.0000 41.8696 35.0824 1.788 47.318.0000 9.3366 6 Navarro eye model 2.0900 NOTES Positive radiusindicates the center of curvature is to the right Negative radiusindicates the center of curvature is to the left Dimensions are given inmillimeters Thickness is axial distance to next surface The Navarro eyemodel is described in J Opt Soc Am A. 1985 August; 2(8): 1273-81.Accommodation-dependent model of the human eye with aspherics. NavarroR. Santamaria. J. Bescos J.

TABLE 5 ASPHERIC CONSTANTS Z = ((CURV)*Y²)/(1 + [1 − (1 +K)*(CURV)²Y²]^(1/2)) + (A)*Y⁴ + (B)*Y⁶ + (C)*Y⁸ + (D)*Y¹⁰ ASPHERIC CURVK A B C D A(1) −0.01070741 −1.00000000 1.41214E−06 −2.35725E−111.98134E−13 0.00000E+00 REFERENCE WAVELENGTH = 587.6 NM SPECTRAL REGION= 486.1-656.3 NM

TABLE 6 INFINITE CONJUGATES EFL = −30.6757 BFL = 12.0923 FFL = −34.3970F/NO = −11.4806 IMAGE DIST = 12.0500 OAL = 226.7496 PARAXIAL IMAGE HT =10.5974 SEMI-FIELD ANGLE = 24.7750 ENTR PUPIL DIAMETER = 2.0000 DISTANCE= 0.0000 EXIT PUPIL DIAMETER = 1.3351 DISTANCE = −8.3847

The second embodiment 500 of the relay system of the inventionstructured as described in the above Tables 4, 5 and 6 is presented inFIG. 4 and has an effective focal length of 30.67 mm (modulus value),which results in formation of an image with a (paraxial) height of about10.6 mm, and is corrected well for lateral color aberration(s). Theembodiment of the lens system according to the idea of the inventioncontains only one, single aspheric surface A(1), which providespractical advantages (such as reduced costs). As shown in FIG. 4 , thesecond embodiment contains a first lens group G1 and a second lens groupG2. The first lens group G1 includes lens elements 4 and 5, and thesecond lens group G2 includes lens elements 1, 2 and 3. The Navarromodel of the eye is also shown in combination with the relay system 500.The second lens group G2 includes a first meniscus lens element 1 havinga negative dioptric power and in optical contact with the biconvexpositive lens element 2, and the element 3 having a positive opticalpower and an aspheric surface A(1) and spatially separated from thecombination of the elements 1 and 2. The second lens group G2aggregately possesses positive optical power, overriding the negativeoptical power of the element 1. The first lens group G1 contains apositive lens element 4 and a second meniscus lens element 5 concave tothe eye side, and has aggregately possesses positive optical power. Thefirst lens group G1 is positioned close to the eye to be inspected, asshown by the Navarro model of the eye in FIG. 4 .

FIG. 5 contains spot diagrams representing the effect of defocussing,while imaging an object with the second embodiment 500 of the invention,as a function of field position (expressed in degrees). The secondembodiment is also shown to compensate for the aberrations of the(Navarro model) eye (at 2 mm eye pupil diameter, the healthy human eyeis almost diffraction-limited) and provides close to diffraction-limitedresolution across the entire 80 degree FOV. As convincingly evidenced bythe spot diagrams falling within the Airy disk curve for each of thewavelengths, aberrations are substantially corrected over the wholevisible spectrum, but are even smaller at the red end of the spectrum(where the backscattered light from the retina is about five timesstronger than that in the blue, which is operationally preferred duringthe imaging of the retina). Such diffraction-limited performance acrossthe visible spear urn critically and advantageously distinguishes theproposed invention from the related art. In practice, the proposeddesign of the optical system is such that diffraction-limited imaging ofthe retina is effectuated by balancing of optical aberrations typicalfor an average eye with those of the eye piece portion of the embodimentof the invention.

For each of the first embodiment and the second embodiment, valuesrelated to the focal lengths of the first lens group G1 and the secondlens group G2 are shown below.

Embodiment 1

Focal length of Group 1 (eyepiece): f1=32.3

Focal length of Group 2 (objective): f2=34.4

Paraxial magnification: f2/f1=1.07

Embodiment 2

Focal length of Group 1 (eyepiece): f1=38.0

Focal length of Group 2 (objective): f2=53.0

Paraxial magnification: f2/f1=1.4

With respect to the relation between the wide angle retinal image sizeand the size of the image sensor there are two possible cases. In case1, the magnification is chosen such that the 80 degree field of viewentering the eye is imaged on to the camera to fill the diagonal of thescreen (i.e., the size of the image sensor), as shown in FIG. 6A. Thishas the advantage that all of the camera pixels are used, but thedisadvantage of losing some of the 80 degree field of view at the top,bottom and sides.

In case 2, the magnification is chosen such that the 80 degree field ofview entering the eye is imaged on to the camera screen (i.e., the sizeof the image sensor) to fill the short dimension of the rectangularscreen, as shown in FIG. 6B. This has the advantage that the whole 80degree field of view is seen, but the disadvantage that not all of thecamera pixels are used. This is the more common fundus camera situationbut the two cases show that the invention can be applied to eithersituation by selecting the appropriate magnification close to 1.0, inthe range 1.0 to 2.0.

A specific implementation of the invention can also be structured totake advantage of fundus imaging with a dual-lens (or, generally, amultiple-lens) cellphone camera. For example, if a cellphone has asecond camera lens with a different focal length (for example, twice thefocal length of the first lens of the cellphone), then—if and when thecellphone is shifted laterally or transversely with respect to theafocal relay of the invention to optically (axially) align the secondlens with the afocal relay—the central angular portion of the retina(the one corresponding to the cellphone lens having the smaller FOV ascompared to the FOV of another lens of the cellphone) can be imaged at ahigher resolution. This is advantageous for more closely studying thefoveal region and optic nerve, while retaining the capability to capturethe whole retina by stitching to the short focal length camera.Alternatively, in this case, image stitching could be used with thelonger focal length lens, to cover an 80 degree field of view or more athigher resolution.

The scope of the invention advantageously accommodates a situation inwhich a mobile device has multiple lenses (optical systems) disposednext to each other (as a 1D or 2D array of lenses, for example) andhaving different focal lengths (and, therefore, different FOVs). Here,the embodiment of FIG. 1 can be integrated with the back side of themobile device through a contraption or positioner (driven mechanicallyor otherwise, for example, with the use of an electrical motor)configured to laterally reposition the embodiment in a planeperpendicular to the optical axes of such multiple lenses whilemaintaining the working (axial) distance between the embodiment and theplane in which the multiple lenses are disposed. When the embodiment isso translated to be co-axially disposed with a first lens of thecellphone camera, the optical conjugation is established between the EPof the eye and the EP of the first lens and the 1× imaging of the retinawith the use of the telescope of the invention and the first first lensis advantageously enabled. When, at the next step of operation, theembodiment is translated to be co-axially disposed with a second lens ofthe cellphone camera, the optical conjugation is established between theEP of the eye and the EP of the second lens and the 1× imaging of theretina with the use of the telescope of the invention and the secondlens is enabled. As a result of a multi-step (for example, N>1)repositioning, an N-position-zoom imaging system is practicallyimplemented. It is appreciated that during so-configured imaging of theretina, the imaging of the retina with higher resolution is achieved (inthe middle of the stitched image) when the cellphone lens having asmaller FOV is optically and mechanically cooperated with the embodimentof the afocal relay.

Furthermore, usually, the user will not have their spectacles on whenpictures are taken, so a +/−10 Diopter adjustment can be provided byfocusing the lenses closest to the eye—the eyepiece-based on the user'sprescription. The camera's focusing system will adjust for fine focus.

According to the foregoing embodiments, a low-cost eye fundus camerahaving a simple and small-sized configuration is enabled. Further,compared to a conventional eye fundus camera using an attachment lens,it is clear that a superior eye fundus image can be obtained across afield of view that is approximately twice as broad and across a broadwavelength region. Further, when a multiple-lens cellphone camera isused, the degree of freedom of the field of view and the resolutionperformance increases.

Disclosed aspects, or portions of these aspects, may be combined in waysnot listed above. Accordingly, the invention should not be viewed asbeing limited to the disclosed embodiments.

In the following, a third embodiment is explained with reference to FIG.7 .

As shown in FIG. 7 , attachment 22 is a relay optical system that relaysthe pupil of subject eye 150 to the pupil position of the optical systemof image capture portion 214 of cellphone 20, and is provided with firstpositive lens group G1 and second positive lens group G2. First positivelens group G1 and second positive lens group G2 have the same opticalaxis and substantially form an afocal system. The pupil of subject eye150 is relayed to the pupil of the optical system of image captureportion 214 of cellphone 20 by the combination of the first positivelens group G1 and the second positive lens group G2.

The afocal relay of the invention, as an afocal attachment goes on thefront of the cellphone camera lens. In this case, it serves to relay thecellphone camera pupil to the iris (pupil) of the patient.

When the afocal relay attachment 22 which is composed of the firstpositive lens group G1 and the second positive lens group G2 is disposedbetween subject eye 150 and the optical system disposed at the frontside of image capture portion 214 of cellphone 20, as shown in FIG. 7 ),the configuration is such that the eye side focal position of the firstpositive lens group G1 is aligned with the pupil position of subject eye150, and such that the focal position, at the side of cellphone 20, ofsecond positive lens group G2 is aligned with the pupil position of theimage capture optical system of cellphone 20. According to theconfiguration above the combination of the first positive lens group G1and the second positive lens group G2 forms a conjugate relationshipbetween the pupil of the subject eye and the pupil of the externaloptical system.

When the afocal attachment 22 including first positive lens group G1 andsecond positive lens group G2 is disposed, as shown in FIG. 7 , at aposition at which its optical axis is aliened with the optical axis ofthe image capture optical system of cellphone 20, image FI of the eyefundus of subject eye 150 is formed between the first positive lensgroup G1 and the second positive lens group G2.

The first positive lens group G1 includes, in the order from the side ofthe subject eye, positive meniscus lens 320, which has a concave surfacefacing the side of the subject eye, and positive lens 340, and thesecond positive lens group G2 includes, in the order from the side ofthe subject eye, positive lens 330 and meniscus lens 310, which has aconvex surface facing the side of the subject eye.

Positive meniscus lens 320, which has a concave surface facing the sideof the subject eye, is not limited to the configuration shown in FIG. 7, and may have the configuration shown in FIG. 2 , being a compound lensincluding positive meniscus lens 6, which has a concave surface facingthe side of the subject eye, and meniscus lens 5, which has a concavesurface facing the side of the subject eye.

The meniscus lens 310 of the second positive lens group G2, which has aconvex surface facing the side of the subject eye may, as shown in FIG.7 , be a compound lens of biconvex positive lens 310A and biconcavepositive lens 310B cemented with each other. Further, it is possible, asappropriate, to adopt an aspherical surface as the shape of the lenssurface, and in the second example, an aspherical surface is provided atthe convex surface, at the side of the subject eye, of the biconvex lensof the second lens group G2.

When f1 is the focal length of the first lens group G1, f2 is the focallength of the second lens group G2, and D is the principal planeinterval of both lens groups G1, G2, it is preferable that the followingcondition is substantially satisfied.

f1+f2=D

When, as described above, first positive lens group G1 and secondpositive lens group G2 substantially form an afocal system, it ispreferable that the following condition is satisfied.

0.9<f2/f1<2.2

In addition, in terms of practical use, the condition 1.0≤f2/f1<2.0 ispreferably satisfied.

It is preferable that the focal length f1 of the first lens group G1 andthe focal length f2 of the second lens group G2 satisfy the followingconditions.

30 mm<f1<50 mm

30 mm<f2<60 mm

The angle of view of the second lens group G2 at the side of the opticalsystem of cellphone 20 includes, and preferably matches, the angle ofview of the optical system of cellphone 20. The image of the imagecapture field of view (FOV) of the subject eye fundus corresponding tothe angle of view of the first lens group G1 is transferred to theoptical system of cellphone 20 via second lens group G2.

The 1× magnification of the relay optical system of attachment 22 of allthe foregoing embodiments is the ideal for aberration correction;however, as mentioned above regarding the numerical conditions, a largerfield of view than the cellphone camera is achieved by introducing asmall amount of magnification, and the design is still able to achievefavorable aberration correction. A larger field of view is beneficial inthat many pathologies of the retina can be seen within the 80 dg. fieldof view, and it is possible to switch to the cellphone telephoto lenscamera to look in more detail at the central 40 dg. of the retina.

Further, attachment 22 is provided with a power source 380, a lightsource 362, which is supplied with power by the power source 380, and abeam splitter 372, which reflects light emitted from the light source362 toward the side of second lens group G2 and passes light reflectedfrom subject eye 150, via second lens group G2, through to cellphone 20.

In an image capture mode, which is described below, light emitted fromthe light source 362 is reflected, at the beam splitter 372, toward theside of second lens group G2 and arrives at the eye fundus of subjecteye 150 via first lens group G1. Light that reached the eye fundus ofsubject eye 150 is reflected at the eye fundus, and the reflected lightarrives at beam splitter 372 via the first lens group G1 and the secondlens group G2, passes through the beam splitter 372, and arrives at thecellphone 20. The pupil of subject eye 150 is relayed to the pupil ofthe optical system of image capture portion 214 of the cellphone 20 bythe first positive lens group G1 and the second positive lens group G2.

Next, a fourth embodiment is explained. Since the fourth embodimentshown in FIG. 8 has similar portions to the third embodiment, the samereference numerals are assigned to the similar portions and explanationthereof is omitted, while the different portions are explained.

As shown in FIG. 8 , the afocal attachment 22 has, in addition to thefirst lens group G1 and the second lens group G2, a light source 362 anda power source 380 for the light source 362. Divergent light from lightsource 362 is collimated by a condenser lens 364. Then, the collomatedlight is incident at diffuser 366 and becomes divergent light, andirradiates ring diaphragm 368, which has a ring-shaped aperture. Lightthat passes through this ring-shaped aperture is reflected at beamsplitter 372, and is guided to subject eye 150 through the second lensgroup G2 and the first lens group G1. Further, due to the action of thesecond lens group G2 and the first lens group G1, an image of thering-shaped aperture of ring diaphragm 368 is formed on the pupil of thesubject eye and irradiates the eye fundus of the subject eye.

Next, a fifth embodiment is explained. Since the fifth embodiment shownin FIG. 9 has similar portions to the third embodiment, the samereference numerals are assigned to the similar portions and explanationthereof is omitted, while the different portions are explained. As shownin FIG. 9 , the afocal attachment 22 includes contact 382, which isconnected to light source 362. Cellphone 20 includes a contact 20C,which is connected to the battery (not shown) of the cellphone 20. Whenthe afocal attachment 22 is attached to cellphone 20, the contact 382 ofthe attachment 22 and the contact 20C of the cellphone 20 are connected.Since, as described above, the contact 382 is connected to the lightsource 362 and the contact 20C of the cellphone 20 is connected to thebattery (not shown) of the cellphone 20, power from the battery (notshown) of the cellphone 20 is supplied to the light source 362 via thecontact 20C and the contact 382.

In the fourth embodiment (refer to FIG. 8 ), it would be acceptable toomit the power source 380, and to provide the contact 382 at theattachment 22, and provide the contact 20C at the cellphone 20, suchthat when attachment 22 is attached to the cellphone 20, the contact 382of the attachment 22 and the contact 20C of cellphone 20 are connected,and power from the battery (not shown) of the cellphone 20 is suppliedto the light source 362 via the contact 20C and the contact 382.

While all of the examples described above use the beam splitter 372, itwould be acceptable, in order to efficiently utilize the light fromlight source 362, to provide a polarizing beam splitter instead of thebeam splitter 372, to dispose a polarizer between light source 362 andthe polarizing beam splitter, and to provide an analyzer between thepolarizing beam splitter and the cellphone 20. Further, it would bepossible to insert a quarter wave plate between the second lens group G2and the polarizing beam splitter, and adopt a configuration thatsupplies circularly polarized light to the subject eye.

Next, referring to FIG. 10 , the electrical configuration of all of theabove-described examples of cellphone 20 is explained. As shown in FIG.10 , the cellphone 20 is provided with computer 200. Computer 200 isprovided with CPU 202, ROM 204, RAM 206, and input and output (I/O) port208. CPU 202, ROM 204, RAM 206, and I/O port 208 are mutually connectedvia bus 210. I/O port 208 is connected to auxiliary storage device 212,image capture portion 214, speaker 216, display portion 218,communication portion 220, home button 222, image capture button 224,and autofocus mechanism 226.

Next, referring to FIG. 11 , a method of use of attachment 22 andcellphone 20 is explained.

In Step 402, a user mounts attachment 22 at cellphone 20. When the powersource switch of cellphone 20 is turned on, an eye fundus image captureapplication starts up in Step 404. In Step 406, the user holds their eyeat the image capture position of image capture portion 214.

In Step 408, by turning on home button 222 of cellphone 20, CPU 202initiates image capture mode. When image capture mode is initiated,image capture portion 214 captures an eye fundus image via attachment22.

In Step 410, CPU 202 adjusts autofocus mechanism 226, automaticallyadjusts the focus, and when the focus is automatically adjusted,determines whether or not the eye fundus image capture range of imagecapture portion 214 is appropriate. Specifically, the position of thepupil of subject eye 150 is detected within the eye fundus image capturerange of image capture portion 214 from the respective pixel values ofthe image data of the eye fundus image and from threshold values fordistinguishing between a pupil portion and a peripheral portion. Bydetermining whether or not the detected position of the pupil is withinthe image capture range, it is determined whether or not the imagecapture range is appropriate.

When it is determined that the eye fundus image capture range isinappropriate in Step 410, CPU 202 emits an audio instruction to changethe hold position of cellphone 20 via speaker 216 in Step 412. Forexample, when the pupil position is at a higher position than the imagecapture range of image capture portion 214, “please raise the cellphone”is audio output via speaker 216. Instead of the audio output of “pleaseraise the cellphone”, or together with this audio output, “please raisethe cellphone” may be displayed at display portion 218.

When it is determined that the position of the user's eye fundus isappropriately positioned in the image capture range of image captureportion 214, CPU 202 displays an image capture instruction at displayportion 218 in Step 414. The user, having seen the image captureinstruction displayed at display portion 218, turns on image capturebutton 224. The image capture instruction is not limited to beingdisplayed at display portion 218, and an image capture instruction maybe audio output via speaker 216 instead of, or in addition to, thisdisplay. When image capture button 224 is turned on, CPU 202 detectsthat image capture button 224 has been turned on in Step 416. When ithas been detected that image capture button 224 has been turned on, theeye fundus image captured by image capture portion 214 is stored atauxiliary storage device 212 in Step 418, and, in Step 420, an imagesignal of the eye fundus image is transmitted to eye fundus image server250 via communication portion 220.

Omitting the processing of Steps 414 and 416 when it has been determinedthat the position of the user's eye fundus is appropriately positionedwithin the image capture range of image capture portion 214, CPU 202stores the eye fundus image captured by image capture portion 214 atauxiliary storage device 212 in Step 418, and transmits an image signalof the eye fundus image to eye fundus image server 250 via communicationportion 220 in Step 420.

In all of the examples explained above, the cellphone 20 is providedwith a single optical system (image capture lens system (camera lens));however, the technique of the present disclosure is not limited thereto,and plural optical systems corresponding to plural angles of view may beprovided. For example, in order to handle cases in which a peripheralportion surrounding the central portion of the eye fundus is to becaptured in addition to the central portion, cellphone 20 may beprovided with a first optical system for wide-angle use and a secondoptical system for standard use having a smaller angle of view than thewide angle. In a first mode that captures an image of the centralportion and the peripheral portion of the eye fundus, an image of thecentral portion and the peripheral portion of the eye fundus would beformed at image capture portion 214 via the first optical system. In asecond mode that only captures an image of the central portion, an imageof only the central portion of the eye fundus would be formed at imagecapture portion 214 via the second optical system.

REFERENCE SYMBOL LIST

-   -   20 Cellphone    -   22 Attachment    -   G1 First lens group    -   G2 Second lens group    -   320 Meniscus lens    -   320A Meniscus lens    -   320B Meniscus lens    -   340 Positive lens    -   33 Positive lens    -   310 Meniscus lens    -   310A Biconvex lens    -   310B Biconcave lens    -   320 Positive meniscus lens    -   320A Positive meniscus lens    -   320B Meniscus lens

1. An optical imaging system, comprising: a first lens system housed ina body of a mobile telecommunication device, said first lens systemhaving a first optical axis, a first entrance pupil fixed in space in areference plane associated with said body, and a first focal length; andan optical telescope providing a diffraction-limited imaging within aspectral range from at least 486 nm to at least 656 nm; wherein theoptical imaging system is configured to image, when the opticaltelescope is inserted between the first lens system and an entrancepupil of a visual system of an eye (EPE), the EPE onto the firstentrance pupil and vice versa with a substantially unit magnification.